1. Field of the Invention
This invention relates to the catalytic hydrogenolysis of fluorohalocarbons or fluorohalohydrocarbons and more particularly to carbon supported Group VII or Group VIII metal catalysts and their use in the hydrogenolysis of fluorohalccarbons or fluorohalohydrocarbons.
2. Background
A number of chlorinated fluorocarbons are considered to be detrimental toward the Earth's ozone layer. There is a world-wide effort to develop materials that can serve as effective replacements. For example, 1,1,1,2-tetrafluoroethane (HFC-134a), a fluorohydrocarbon containing no chlorine, is being considered as a replacement for dichlorodifluoromethane (CFC-12) in refrigeration systems because of its zero ozone depletion potential. There is thus a need for manufacturing processes that provide fluorocarbons that contain less chlorine.
One method of reducing the chlorine content of halogen substituted hydrocarbons containing chlorine as well as fluorine is reacting organic starting materials containing chlorine and fluorine with hydrogen at elevated temperature in the presence of a hydrogenation catalyst (e.g., supported Group VII or Group VIII metal catalysts). British Patent Specification 1,578,933 discloses, for example, that HFC-134a can be prepared by the hydrogenolysis of 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a) or 1,1,1,2-tetrafluorochloroethane (HCFC-124) over palladium on carbon or palladium on alumina hydrogenation catalysts. There remains a continued interest in providing improved hydrogenolysis processes for the manufacture of HFC-134a as well as other fluorohydrocarbons and fluorohalohydrocarbons.
Techniques for enhancing the activity of Group VIII metal hydrogenolysis catalysts have been disclosed. The catalyst improvements described in Eur. Pat. Appln. 347,830 and Jap. Pat. Appln. 1-128,942 are achieved by the addition of other elements, such as Group IB, lanthanum, lanthanide elements, and rhenium to the Group VIII metal catalysts. The additives are said to prevent sintering and also increase the activity and the mechanical strength of the catalysts.
Palladium catalysts are considered generally to be resistant to catalyst poisons (Augustine, "Catalytic Hydrogenation" Marcel Dekker, inc., N.Y, 1965, page 38); although Rylander "Catalytic Hydrogenation over Platinum Metals," Academic Press, New York, 1967, p. 19, reveals that all types of metal cations may cause drastic inhibition of platinum metal catalysts. However, there is no way of generalizing what the effect of any particular cation will be. Furthermore ions such as Na.sup.+, K.sup.+, and Ca.sup.2+ have been reported to be nontoxic to platinum (J. T. Richardson, "Principles of Catalyst Development," Plenum Press, New York, 1989, P. 206) and in view of the above are considered to be non-toxic toward palladium.
U.S. Pat. No. 2,942,036 claims a process for hydrogenating 1,2,2-trichloropentafluoropropane over a palladium supported on activated carbon catalyst. The carbon support may be treated prior to depositing palladium on it with aqueous HF. The purpose of this treatment is to remove any silica from the carbon.
Various processes using catalysts containing acid-washed carbon have been studied. A. A. Goleva et al., Russ. J. Phys. Chem., 44.sup.2, 290-1 (1970) disclose the dehydrochlorination of 1,1,2,2-tetrachlorethane to trichloroethylene and HCl using activated charcoal as the catalyst. Activated charcoal treated with hydrochloric acid proved to be more active than an untreated specimen for the production of the olefin, trichloroethylene. M. Biswas et al, J. Macromol. Sci., Chem., A20(8), 861-76 (1983) disclose that the activity of carbon black catalysts for the polymerization of N-vinylcarbazole can be enhanced by treatment with protonic acids such as HNO.sub.3, H.sub.2 SO.sub.4 and HClO.sub.4. Chem. Abst. 80 (25): 145470q and Chem. Abst. 80 (25): 145469w disclose an increase in yields of unsaturated glycol diesters when the active carbon catalyst support was treated with HN03 compared with untreated carbon.